1. Field of the Invention
The present invention relates to a liposome, a proteoliposome, a biochip, and a method for producing the liposome and the proteoliposome.
2. Description of the Related Art
In natural cell membranes, there exist microdomains (lipid rafts) composed of mixed lipid including phospholipids of different chain lengths and molecules other than phospholipids, such as cholesterol. The lipid rafts are considered to be the center for inserting receptor proteins and seem to play a key role in signal transduction. More specifically, the lipid rafts are considered to have a function of organizing or separating neurotransmitter receptors so as to increase or decrease the signal transduction in central nervous system synapses.
The structure of the lipid raft in a cell membrane is not static, but rather shows a change in physiological state. Concretely, the lipid rafts of the synaptic membrane change by stimulation due to bleeding or food intake. Furthermore, organization of receptor proteins of the lipid rafts immediately shows a change according to an ambient environment of the lipid bilayer membrane (hereinafter, also may be referred to as a “lipid membrane”), and this is believed to be so because the change in a lipid raft structure has an effect on the density of receptor proteins in the lipid raft.
As mentioned above, since the lipid rafts play an important role in signal transduction, the structure and function have been examined extensively by forming a natural lipid raft-like lipid structure (hereinafter, referred to as a “raft-like structure”). The raft-like structure is formed by including molecules other than lipid, such as cholesterol (for example, see Rodrigo F. M. de Almeida, Luis M. S. Loura, Alexander Fedorov and Manuel Prieto, J. Mol. Biol., 346, 1109-1120 (2005) and Wattana Weerachatyanukul, Ira Probodh, Kessiri Kongmanas, Nongnuj Tanphaichitr, Linda J. Johnston, Biochimica et Biophysica Acta, 1768, 299-310 (2007)).
However, for the methods described in Rodrigo F. M. de Almeida, Luis M. S. Loura, Alexander Fedorov and Manuel Prieto, J. Mol. Biol., 346, 1109-1120 (2005) and Wattana Weerachatyanukul, Ira Probodh, Kessiri Kongmanas, Nongnuj Tanphaichitr, Linda J. Johnston, Biochimica et Biophysica Acta, 1768, 299-310 (2007), the temperature upon mixing had to be high to some extent so as to sufficiently mix molecules other than lipid, like cholesterol, with lipid, and thus the operation became complicated. In addition, in the case of a high molecular weight molecule such as cholesterol, it has been particularly difficult to reconstitute membrane proteins in the raft-like structure, thereby making it difficult to prepare a specimen having membrane proteins. Moreover, the production cost became expensive due to the use of molecules other than lipid.
Therefore, a method for easily forming a raft-like structure without using molecules other than lipid, such as cholesterol is required.